This invention generally relates to high voltage particle accelerators and is particularly directed to the utilization therein as the high voltage source of a class of polycrystalline ferroelectric ceramic materials which have been discovered to produce high voltages upon the application of incident light thereto.
As background, and with particular reference being had to the detailed disclosure in U.S. Pat. No. 3,855,004 and to my copending CIP application Ser. No. 533,365, it has been discovered that an arrangement of an initially polarized polycrystalline ferroelectric ceramic material such as is schematically shown in FIG. 1 of the application drawings produces steady high voltages upon the application thereto of an incident source of electromagnetic radiation, such as light. The magnitude of the voltages produced has been found to be directly proportional to the remanent polarization of the ferroelectric ceramic material, such polarization being effected by the application across said ferroelectric ceramic material of an initial voltage pulse, the polarity of the initial voltage pulse and thus the polarity of the remanent polarization within the ferroelectric ceramic material fixing the polarity of the photovoltage developed. The magnitude of the voltage developed is proportional to the length l of the sheet of material provided. The magnitude is also proportional to the number of grains per unit length within the material.
When illuminated at intensity levels such as that produced by direct sunlight or such as that produced by a fluorescent lamp, or such as produced by intense monochromatic or polychromatic laser radiation, for example, these ferroelectric ceramic materials will behave as voltage sources in series with a high output resistance and with the output resistance of the device varying in accordance with the wave length of the incident illumination and decreasing as the intensity of illumination increases. The open circuit photovoltages produced by such devices is extremely high. For example, and with specific reference to the composition Pb(Zr.sub..65 Ti.sub..35)O.sub.3 with 7% of the lead substituted by lanthanum, when composed of 2-4 micron grains produces, when illuminated as shown in FIG. 1, 1500 volts for every centimeter of length between the electrodes. A single 1.sub.cm square unit thus directly produces 1500 volts.
The extremely high voltages capable of production by such ferroelectric ceramic materials find direct utilization in devices which are alternatives to apparatus presently utilized for the generation of extremely high DC voltages at low currents, such as the Van de Graaf belt machine in which high voltages are produced by mechanically moving electric charges, and in which such high voltages are utilized to accelerate a beam of charged particles.